U.S. Pat. No. 6,101,991 describes in FIGS. 4 to 6 thereof a carburetor for a two-stroke engine in which the outlet side of the fuel-air mixing passage is connected to separate relatively lean and rich fuel channels of an engine intake duct. However, except when the throttle shutter is fully open, FIG. 6, the channel separation does not extend upstream into the carburetor itself. It is difficult to calibrate a carburetor that feeds two such channels if they are allowed to communicate with each other in the carburetor during idle and intermediate throttle shutter positions of the carburetor.
Accordingly, the present invention provides a carburetor for feeding separate lean and rich channels of an engine intake duct, the carburetor comprising a body having a mixing passage with an air intake side and an engine outlet side, a throttle shutter rotatable about an axis transverse the mixing passage, and a partition located within the mixing passage upstream of the throttle shutter, the downstream edge of the partition being adjacent the throttle shutter axis whereby in use of the carburetor the partition defines an extension of the lean and rich channels upstream of the throttle shutter, the partition providing substantial isolation between the lean and rich channels for all rotational positions of the throttle shutter.
Preferably the carburetor further includes a choke shutter located upstream of the throttle shutter and rotatable about a further axis transverse the mixing passage, the upstream edge of the partition being adjacent to the axis of the choke shutter.
The invention provides a more effective separation of the lean and rich fuel channels for all throttle shutter positions and therefore reduces the number of variables when calibrating the carburetor.